Hi Mette,
If you want to capture exactly what is visible on your screen iShowU
is a cheap application that works well with a Mac. Fraps might work
for you if you are on a Windows computer, but in the free version the
Fraps logo will be captured as well. You can find a (30 days?) free
test version of iShowU on the web.
But there are also ways to log chat only. It is an option that is
build-in in the game viewer (at least in WoW or virtual environments
such as Second Life).
Hope that helps,
Tjarda Sixma
Tjarda Sixma MA
sixma.vijselaar at planet.nl
www.vijselaarensixma.nl
J. de Wittlaan 22
6828WH Arnhem
The Netherlands
+ 31.26.4421612